Meteor Ablation as Origin for the D-region Ledge in Electrical Conductivity
Yen-Jung Wu1 , Earle Williams2 , Rue-Ron Hsu1
1Department of Physics, National Cheng Kung University, Taiwan
2Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA
The electron density ledge in the 80 to 90 Km altitude range has been identified since 50s by the rocket soundings, which is the abrupt increase in the mesosphere and lower thermosphere (MLT ) region with scale height less than 500 m. The ledge is necessary to VLF propagation as this altitude is also the electric field reflection height of the VLF waves that satisfy the conductivity current equals to the displacement current, the reflection height of whole range of the VLF waves are able to be confined at the 80-90km altitude in the flat region of the electron density profile.
In the recent decade, the existence of meteoric smoke particle in the MLT has been identified as the sink of electrons because of the high electron affinity. The micro-sized meteors with re-entre speed ~ 15 km/s ablate at the height between 85- 90km is the source of the nano-sized meteoric dust , which the concentration is in the same order of electron density that serves to scavenge the electrons than hence the ledge. As long as the concentration of atomic oxygen increases abruptly the range of altitude, it gives the chance for electrons to attach on the meteoric dust firmly, despite the larger collision rate of molecular nitrogen and oxygen. The key role for meteor ablation in this ionospheric context has not received due recognition because neither the meteoric dust nor the meteors that create it are readily detectable by remote sensing, and in situ observations of the mesosphere are scarce.